Vacuum tube audio amplifiers generally utilize push-pull output configurations as the most economical method of producing ample power. The benefits of push-pull are well known in the art and require no repetition herein. It is sufficient to say that commercial amplifiers offering power levels even as low as 15 watts will use a push-pull pair of output tubes, though one larger tube in a single-ended configuration could also provide similar power. It can be safely asserted that virtually all commercial audio amplifiers providing more than 20 watts are of the push-pull variety.
In contrast, single-ended vacuum tube output sections have previously been used mostly in 5 to 8 watt so-called “beginner” guitar amplifiers, which offer a stark economy of overall design. Nevertheless, such low powered units occasionally find favor in recording studios or small apartment-sized venues. In such circumstances, their lower power can become a virtue, providing desirable “power amplifier clip” at low volume levels. Many guitarists claim distortion generated in the power section is more legitimate (due to its historical roots), and is more musically pleasing compared to preamplifier overdrive saturation.
Without discussion of the relative merits of the two, power amplifier distortion remains dependent on the power capability provided and therefore suffers from a lack of versatility regarding loudness. The desired distortion characteristics and the output loudness of an amplifier are so intimately related as to be inseparable and overcoming that limitation is what initially spurred the creation of cascading preamplifier gain structures with separate gain and level attenuation, such as shown in the Smith U.S. Pat. No. 4,211,893, the contents of which are incorporated herein by reference.
The guitar amplifier design as demonstrated by Smith U.S. Pat. No. 4,211,893 ushered in the “modern era” of guitar amplification and provided the live musician with the ability to set a high-gain sound rich in distortion characteristics independent of its volume level and the ability to switch alternately and selectively to an undistorted clean sound. In order to achieve this goal, distortion is created within the preamplifier section via overdrive saturation, and though it may mimic power amplifier clip, the two are not the same.
As playing styles and circumstances have evolved over the years, a greater emphasis is now placed on recording, particularly home recording, and on live performance venues of small to medium size. In the prior art, an amplifier capable of producing genuine power amplifier distortion at a volume suitable for home recording or practicing would not be usable in a live performance and vice versa.